Fix TLE XML corruption and prevent Aris crash during proof evaluation

[jaybutani1793]

Problem

The provided TLE file contains corrupted XML entries (notably in lines n=5 and n=30) due to incorrect encoding and invalid characters (e.g., ÿ).
Although the file loads in the web version (with console warnings), GNU Aris (Qt version) crashes or hangs when evaluating the proof.

Root Cause

• Invalid XML content in r attributes (e.g., r="dÿ")
• Corrupted characters introduced during file saving
• Missing validation in proof evaluation:
  • Invalid references
  • Self-references (e.g., l="8")
  • References to non-existent steps
• These lead to invalid memory access, causing segmentation faults

#1. XML Fixes

• Removed invalid characters (ÿ)
• Fixed malformed attributes
• Ensured proper UTF-8 encoding

2. Reference Fixes

• Removed references to non-existent entries
• Eliminated self-referencing steps
• Fixed invalid dependencies

#3. Stability Improvements

• Cleaned proof structure to prevent:
  • Infinite loops
  • Invalid pointer access

Testing

• ✅ File loads correctly in web version (no console errors)
• ✅ File loads in aris-qt.exe
• ✅ Proof evaluation runs without crash or hang
• ✅ No segmentation fault observed

[kovzol]

Thanks, I'll check it soon.

[faresbakhit]

Looks good to me